knudsen



May 30, 1950 K, J. KNUDSEN ELECTRICAL METER 2 Sheets-5heet 1 Original Filed Sept. 15, 1942 INVENTOR. K J. Knudsen y 1950 K. J. KNUDSEN Re. 23,236

ELECTRICAL METER 7 Original FiLed Sept. 15, 1942 2 Sheets-Sheet 2 INVENTOR. Knu KnuJsen Reissuecl May 30, 1950 UNITED S PAT EN T F F I CE ELEGIRICAL METER KnudJ. Knudsen, Naugatuck, Conn. Original -No.-2;391 ,168, dated December 18, 1945,

10 Claims.

1 This invention relates to a metenfojr indicating [the ratio and direction "ofj' electrical currents and. particularly to a rnete rjof the directicurrent permanent =magn'ettype having moving coils.

One'of the principal'objects is top'r'ovidea relatively high sensitivity and accuratem'eter of this general character in which it-is pcssihl'e' to install or remove and replace the assembly as a unitflcomplete in itself, wlthout in any manner disiturbinglordeflecting the magnetic flux through the air igap of'fthe magnetic 'circuitj'the magnet'and core assembly.

Another object is to provide a direct current meter which utilizes boththe'incoming'and: outgoing flux through a core' foractuatingthe "deflectingcoil of a moving coil 'assembly 'so' -that the entire flux established inlthe air gap c'fthe permanent magnet is utilized feffectivelyfor'operating the moving .coi-ll A correlative object 'is.'to lutilizeithesame major flux field that actuates the deflecting coil "tor causing the restoringltorque of the restoring .co'il.

Another object is tokpr ovide such a ratio" meter in which the restoring coilfiis..[actuated] eneryized. by an external. electrical source whichhas a proportional efiect on the "deflecting coil and therefore does not-tendto. changethe position'of the deflecting coil and attached instrument pointer dueto changes in this source.

A specific object is to provide in a high sensitivity meter-abearing screw of a new-design by which-the bearing-is held in place efficiently andsecurely and which is easily operated .for installation, removal, and replacement 'of the moving. coil assembly. i

Another object is to provide a meter of this character in which the electrical zerapoint, i. e. the point at which no-currentl'passes-in the vdeflecting coil, is at the-approximate center of -the indicating scale so that. the amount-of compensationlthat must be made for temfzlerature'is reduced relative to what'is required in a straig ht line instrument for-measuring ilIcurrentsl current and'in .whicha means in the'iorm "cs" acalibrating resistoris providedior maintaining a substantially fixed ratio between-the changes in [conductivity] torque of the defl'ctinglcoil' and restoring coil resultingifrom changes in temperature, wherebylvar-ia "ons indell" tion of the deflecting coil, due" ta-heating ofthe 'defiecting coil, msubsiannany compensated} the set-ting of the instrument pointer is not altered.

7 Another object is to;provideanlinstrument of thislcharactenin whicl'i-separateindependent adjustable means are provided; one for Matter enclosed-in heavy bracketsll appears in the original patent but forms no part of this reissue specification; matter printed' in italics indicates the additions made by reissue setting the instrument to indicate the electrical center at the center of the indicating scale, the other means for-calibrating the full scale, whereby the usual tedious cut and try methods of aidjustment, due to interrelated adjustable means necessitated becausetheflelectrical center is outside of the scale range, are eliminated.

Another object is to provide a meter in which the magnetic assembly and the moving coil assembly each is complete in and of itself whereby the magnetic circuit may be originally magnetized' without the moving coil assembly being installed, thus'protecting the delicate moving coll assembly from any damage caused by the'shock occasioned during magnetization of the mag netic assembly. w

Another object is toarrange the deflecting coil and restoring c011 relativeto a common core so that the same 'flux is {substantially equally] available for both coils [and both can be subjected to the same flux at all positions of mcveeme Another-object is to provide an instrument of this character .which utilizes fewer parts than heretofore found necessary and which maygb assembled ymore readi1y.

Qther objects 'andadvantages-will become apparent from the followingspecification wherein reference is made-to the drawings in which -Fig.-1-is a front elevation of a; meter embodying the, principles of t-hepresent invention, assuming the meter tube-positioned with the indicatingldial exposed upwardly;

- FigJ-Z- is a plan view of the meter illustrated in Figl, with the top' bridge, dial plate, and-coiled flexible connector r'ern'oved ior' clea'rness in rill-ustrttion. i

Fig. L3 isa cross sectional View taken on the line 3--3 in Figsfil "and- 2;

*Figpjlis a horizontal "sectional view taken on a -l'i'ne- Fi'g. {3; V

Figffi is' a "wiring diagram of the meter "connected for operaticn fr0m a variable source of current'to beimeasured;

"Fig." 6 is"alongitudinal"sectional View illustratin g th'e' j ewel'ed "bearing and mounting used in connecticnwith the present invention.

'Ratio'mfeters a e utilized in n ere 11s applicaticnssucnas inmate indication, uel car-pressureflhydr'alulic pressures; difierences in" temperatures, and any other jhenoniena v'vfhich', directly or throughthe interpositionof mechanical or other .means, cai ses prop rthnal variations in current due to change in resistance.

Without intending to limit the present invention to the particular use shown, a preferred embodiment of the invention is illustrated in connection with a remote pressure indicating system for fuel oil pressure, its use for other purposes being readily apparent therefrom.

Referring to Figs. 1 to 4, inclusive, the meter comprises generally a magnetic circuit assembly and a moving coil assembly, each of which is a complete sub-assembly in and of itself so that each sub-assembly can be assembled separately and apart from the other and then the two assembled together easily.

The magnetic assembly is best illustrated in Figs. 1 and 4 and comprises a permanent horseshoe magnet l for which generally channelshaped iron pole pieces 2 are provided. The pole pieces 2 are fixedly secured to a nonmagnetic top plate 3 and thus held permanently in fixed relation with regard to each other and with their bases snugly press fitted in contact with the inner faces of the arms of the magnet l and opening toward, and aligned with, each other.

Secured to the top plate 3 is a soft iron core 4 which is generally in the shape of an annulus with its outer perimeter generally circular but somewhat eccentric to the axis of the central opening so that more iron exists in the rear portion of the core to concentrate the flux [in the air gap of the core] passing between the pole pieces and the said rear portion. The core 3 has an integral rearward extension 5 through which the securing bolts 6 are passed for securing the core to the plate 3, the bolts 6 being of brass or other non-magnetic material. Interposed between the soft iron core 4 and top plate 3 are non-magnetic spacers 7 by which the core is definitely fixed in spaced relation axially and laterally from the pole pieces 2. It occupies the major portion of the space within the limits of the pole faces 2.

Secured to the top plate 3 by suitable screws is a non-magnetic dial plate 8. Mounted on the top plate 3 is a top bridge 9 which is of nonmagnetic material, such as brass or phenolic or other synthetic resin and which is spaced a desired distance above the top plate by suitable integral non-magnetic portions or spacers II.

Carried by the pole pieces 2 and positioned below the lower level thereof, is a bottom bridge l2 of non-magnetic material and which is fixedly secured to the pole pieces 2 by suitable non-magnetic screws and is spaced from the pole pieces 2 by integral non-magnetic offset portions or spacers l3. The bridges 9 and I2 are arranged to support the moving coil assembly of the instrument and the entire structure above described, constituting, with the connecting parts, a magnetic assembly, may be readily made into a rigid unit before the installation of the moving coil assembly. The magnetic assembly provides a fixed magnetic circuit which is complete in and of itself.

The moving coil assembly also is complete in and of itself and comprises a deflecting coil i5 which is wound on a suitable light metal frame I6 and a restoring coil I! which is wound on a light metal frame l8. The coils l5 and IT lie between substantially the same spaced parallel planes and have their axes horizontal and arranged at right angles to each other. The deflecting coil 15 is mounted on suitable upper and lower aligned pivots l9 and 20 respectively. The axisof pivots l9 and 20 is at right angles to and passes through the axis of the deflecting coil 15.

Carried by the upper pivot l9 and movable therewith are a pair of suitable non-magnetic oppositely extending arms 2| on which are carried counter-poise weights of non-magnetic material respectively, the weights, preferably, being in the form of small coil springs 22. Likewise secured to the upper pivot and extending therefrom so as to overlie the dial plate 8 when the coils are installed in operating position in the magnetic assembly is a pointer or indicator arm 23 of non-magnetic material. Suitable electrical connections between the coils and the external circuit are provided, as hereinafter explained, and suitable insulation is provided throughout, all in a well known manner.

The core piece 4, as mentioned, is generally in the form of an annulus, but it is open at the forward portion to provide an air gap, as by spaced termini 4'.

On the upper and lower bridges are aligned bearings for engagement with the pivots l9 and 20 of the moving coil assembly for supporting the moving coil assembly in the magnetic field. The bearings are coaxial with an outer circular portion of the core piece 4 as will be described later.

The deflecting coil I5 is arranged with its axis at right angles to and intersecting the upright pivotal axis and the restoring coil ll extends at right angles from the end of the deflecting coil so as to swing therewith about the pivotal axis. The opening through the deflecting coil is such that the coil surrounds and accommodates with slight clearance the core piece 4. Thus upon rotation of the coil l5 about the pivots l9 and 20, the deflecting coil l5 swings about the core 4, maintaining a uniform spaced relation thereto. It will be seen that the poles 2 and core 4 will produce a predetermined flux pattern which results in a moment, exerted by the coil 15, which has a constant ratio to the current in the coil, for any position of the latter in its path of movemcnt. The terminology substantially uniform cutting relation to flux lines as used herein is intended to define the flux relationship whereby the same number of flux lines is traversed by the coil whatever its angular position within its arc of movement. The restoring coil I! is of the proper size to be received through the air gap of the core piece 4 and has a passage therethrough such that the coil accommodates with clearance first one and then the other of the arms of the core piece 4 as the deflecting coil i5 is swung about the pivots I9 and 20 in opposite directions from the air gap. Thus in all but a neutral position, the one illustrated, both coils are provided with an effective core so that the flux is most efiectively utilized.

The moving coil assembly may be moved as a unit into place in the magnetic assembly and the pivots l9 and 29 connected in proper relation, then the electrical connections made.

In order to better illustrate the cooperation of the elements herein described, the operation of the meter will now be described. Looking first to Fig. 4, according to the structure shown therein, a greater number of flan: Zines passes between the pole pieces 2 and the rear, thicker portion of the core 4 than between the pole pieces and the front, thinner portion of the core. The shape of the pole pieces and core is such however, that as the deflecting coil 15 is moved in a clockwise direction the increase in the number of flux lines which the left-hand portion of the coil traberses is offset by the decrease in. thenumber offluai lines which the right-hand; ROTtiOTL'z of, the. coil traverses, so that the :total: number of; flue: lines traversed by both the left-handund;right-hand portions of the coil remains. substantially. con;- stant, and this condition is true; throughout.- the entire path of movement. of thegdeflecting'coil, either clockwise. or counterclockwise; from the; neutral position shown.

When both the deflecting coil. and; therestor= ing coil are used, the, orgamization of thepoles;2. and core 4, as illustratedzin Figs. 1,2 and 4, produces. a flux. which. causes the deflection..of'th'e. coils to. beilroportional. to the ratio of: theourrent. in the deflecting coil tocurrent in the =restoring' coil, throughout the path. of movement of the: coils. Here; again, as is well; understoodrin: the art, this. result is obtainable; bua given. predetermined pattern of flue: distribution,..which is dependent on the shape, spalcingcandilocation of. the poles and. core. The core and. channel shaped pole piecesshown inFig. 4: render the flux. path substantially uniform. coextensive with. the outermost limits. of the path generated burotating the deflectingcoil through at; least 45 in opposite directions a from. its neutral position; that is,.they are so. related asto causethe coilwhen moved through. 04 90 arc to. betraversed by substantially the same number of lines of force whatever its angular position, thereby to obtain a uniform scale deflection characteristic. The restoring coil 17 in'movingfrom the neutral positionshown in Fig. 4 either clockwise-orcounterclockwise will traverse a progressively greater total number of flux: linesasthe extent of its movement is increased, and the restoring'torque exerted by the restoring coilwillincrealsewith its angular deflection from the neutral position.

The magnetic structure shownin Fig; 4; as provided by the present invention, thus enables both the deflecting and restoring coilsto utilize the major fluccof-the instrument, and enables-the de fleeting coil to traverse a total number of flua: lines which remains substantially unchanged throughout its path of movement while at the same time the restoring coil traversesa'pro-gr'eysively increasing number of fluar-Zin-esas its deflection increases.

As noted above the moving coil assembly of the meter, which is complete in and-ojitself; may be moved as a unit into place within.- themagnetic assembly withoutrelative movement between the pole pieces 2 and core 4, and therefore. without disturbing the permanent flux pattern deter-- mined. by the shape, spacing and relative locations of these latter which provides uniform scale deflection characteristics.

In order to avoid possible breakage of the relatively small Wires of' the coil due to repeatedoscillations, the terminals of the coils which are to. be connected to the externaLcircuit, as. willfhereinafter be disclosed, are preferably connected to Phosphor bronze coiled leads or hair springs. which preferably exert littleror. no resistance tomovement of the moving coil assembly. Eachof these springs is soldered'at one. end, to its par ticu-.-- lar terminal of the coils and, itsother end, is..s.e.-- cured to the. proper terminal oftheexternal circult by soldering or otherwise. In the form illustrated, in which three leads to. the external. circuit arenecessary the hairspringsifl' fil', and 62 are utilized. The springs; of course, are.elec-= trically insulated from'the deviceandelectrically connected to their respective connectors; 64;,

and by'whichzthey are: connected-.to.- the.;ex ternal'circuit.

Inorder to provide-an effective andstable bear.--

in the top' and bottom bridges Bland. l2, respectively, for receiving the pivots l9; and; 2B,; and are aligned with each other and coaxial withrthe; outer circular surfacc3fl (Fig. 4) of thecorepiece'; 4. As illustrated in Fig. 6,.eachofthesebearings;

maycomprise ahollow screw 34 in which is slidably mounted ajewelor other bearing g35, shown;

as centrally socketedto receive thepoinied endotthe associated. pivot. The screw. 34isprovided with shoulders 36 (spun flange) to constrain-the. hearing. from movement,- out': ofthe inner end of the screw. Interposed'between the bearing;. and. the outer. end of thescrew and'abuttingn suitable; shoulder" inside the. screw opposite the bearing; is

a radially expansible. helical coilspring ill which may be of spring brassor. Phosphor; bronzeand;

which urges the bearing 35-against the shoulder I 36; The screw. 3 l is .provided-with apair of;ex-

pension slots 38, or anyappropriate plurality; of slots; which extend longitudinally.. thereof, part: wayxof. the length so that the screwmay expand;

or. bee-compressed, radially as. ibis-operated to force.

the bearing into place. The; spring; 3.-l;; when-in stalled, is under suff cient stressto expandthe slotted portion-of-the screw'radially; orto permit it to contract radially under outward yielding pressure and thus holdit resiliently but, tightly, incontact with its complementary threaded element.

For holding the screw 34 in position, a. regulator lock 39 has internal threads in engagement with the external threads of thescrew. SA-andis riveted or otherwise held in place-for. rotational. adjustment on the associatedbridge. Distortion:

0f the central portionof the regulator (screw 3.4). may be utilized to assure that [the regulator locking screw] it remains in the adjustedv posh tion. Thus the bcaringsof the pivots Iiiand 29 canbe moved toward each other the-proper distance and adjustedv for supporting thamovingl coil assembly with the coils thereof surrounding;

the iron core 4 with substantially equal spaces: between the upper andlower faces oithe core-and. the upper and lower sidesof thecoils-in al1'posi:- tions of. the coil unit or assembly.

Referring next to. Fig. 5.v the wiring diagram;

of the instrument is illustrated and, a; circuit is.- shown fopmeasuring. the. current variation due. to movement-of a resistance controlling element which may be assumed tobe operated by 0111111 85.-

sure. Asillustrated in Fig. 5, therestorin coil; l'! is connectedin one armroiawheatstone bridge. having terminals 411 anddlhterminalJl-I of which. is. a. galvanometer terminalandlill ofv which is, a.v

battery terminal. The deflectingcoil i5 is. connected acrossthe galvanometer. terminal. liand,

the other terminal. i3 Ofthflblidgfi... A resistor isinterposed. between ,the. restoring. coil. l1. and the terminal. 42, and together. withtherestoring.

coil. I] forms, one, arm of the. bridge. A.r esistor M of substantially equal ohmic value is connected. between. the. terminalsAZ. and. 4.3. A calibrating resistor. 4.6 is connectedbntweenihe. galvanom:

eter terminal .4 l. of. thebridge. and ,a battery. tor.-

minal 47 the terminal dlmay. beconnectedtotha negative side. Of the. battery. or. source. of...dir.ec.t. current and. terminal 42" connected. to. the. posiT tivcside.of'thebattery, as-shown. Intcrposcd between the terminals 43 and 41 is an external controlling variable such as a variable resistor 49 which may have an adjusting arm 50 operated by oil pressure or any suitable means to vary the resistor 49. Alternatively, I may use a resistor of high temperature co-efficient capable of changing its resistance with change in temperature as in 'a temperature indicator. Between the terminal 4| and the resistor 45 a calibrating resistor is connected in shunted relation around the restoring coil IT. The calibrating resistor is made from substantially zero temperature coefficient wire, or wire the resistance of which does not substantially change with temperature, and serves to compensate for errors due to changes in ambient temperature. Examples of such wire are manganin and constantan.

The deflecting coil l5 and restoring coil I! may be connected to the cooperating elements of the circuit shown in Fig. 5 partly by means of spiral, current conducting, hairsprings, previously referred to, and shown at 69, El and 62 in Figs. 1 and 3. [Pivoted adjuster arms 63 and 64 are indicated in Fig. 3 as connected to the springs 60 and 62, respectively, and a similar lead in element is shown in Fig. 1 at 65 connected to the hairspring 6!] The connectors 63 and 64 may be in the form of pivoted arms adapted to adjust the associated hair springs, Fig. 3, and the connector 65 shown in Fig. 1 may be also so adapted. One or both adjuster arms can have suitable insulative mountings if necessary to enable the arms to act as electrical conductors. The inner turns of the respective hair springs are connected to termini of the deflecting [coils] coil l5 and restoring coil I! in any suitable manner, such as by connections suggested in Figs. 1 and 3 but not fully shown.

In the structure thus illustrated, the hair springs are so wound that when no current whatever is applied to the device, the pointer or indicating arm 23 is at the left of the indicating dial and the restoring coil H is to the right of the air gap, termini 4, in the core as viewed in Fig. 2.

Upon connection of the battery to the terminals 52 and 41, the indicator 23 moves to the central position on the dial in which position the restoring coil lies in the air gap of the core 4, providing there is no current in the deflecting coil, this being the electrical center of the instrument. Thereafter, with [full negative current] current flowing in one direction in the deflecting coil IS the indicator moves to the left or counterclockwise and with the application of [positive] opposite current moves to the right or clockwise beyond the middle position, thus indicating the current direction and amount of unbalance of the Wheatstone bridge. By the use of the two calibrating resistors 45 and 5], the adjustment for neutral position or electrical center of the scale can be obtained with the resistor 46, while, with the resistor 5|, adjustment for calibrating to the full scale can be obtained, thus eliminating the prior tedious cut and try methods which required that adjustment had to be made simultaneously in some manner because the electrical center was suppressed and outside of the scale range.

Heretofore [non-temperature] zero temperature co-efiicient wire resistors have been used and such resistors have been used in series with the deflecting coil so as to prevent a substantial increase in resistance in the deflecting coil circuit with a consequent reduction in current and error in indication. This naturally reduces the efficiency of the indicating device. In the present invention, the calibrating resistor 5| of zero temperature co-efiicient wire is connected in shunt with the restoring coil H and instead of being for the purpose of preventing an increase in the resistance of the deflecting coil circuit, due to increases in ambient temperature, is used for the purpose of decreasing the current in the restoring coil in a direct ratio to the decrease of the deflecting coil current. In the form shown, for example, when the current through the deflecting coil is decreased due to an increase in ambient temperature, a [corresponding] proportionate decrease in current takes place in the restoring coil in order to maintain a correct pointer position. Without the calibrating resistor 5| and due to the series connection of the resistor 45 with the restoring coil ll, the latter [does] would not receive a [proportional] properly proportioned decrease in current with rise in temperature; [as a result] instead the ratio of the [resistances] current of the two coils would [varies] vary, and the reading of the pointer would not always be reliable. By providing the calibrating resistor 5| in shunt with the restoring coil H, the current through the restoring coil is maintained in a fixed ratio to that in the deflecting coil because a greater [portion] proportion of the current passes through the shunt due to the increase of the resistance of the restoring coil. Thus the restoring eiTect of the restoring coil remains in a fixed ratio to the deflecting effect of the coil I5 with changes in ambient temperature.

In eifect, therefore, the structure operates approximately as though the deflecting coil were subjected to the ambient temperature in the usual manner and had a return spring which in some manner was made operative so that its restoring torque was decreased in a fixed relation to the increase of ambient temperature at any given time due to higher resistance of the deflecting coil upon heating. Thus, where the prior structure sought to reduce the effects of heating of the deflecting coil and thus rendered the current less effective for operating the instrument, in the present structure heat effect is permitted to act upon the restoring coil so as to reduce its restoring efiect and not to resist so greatly the torque of the deflecting coil.

As the moving coil assembly is deflected from the centered position, the restoring coil tends to restore the assembly to the center position with a force which is approximately proportional to the deflection in either direction from center and thus the instrument is in its true electrical sense a zero center galvanometer, even though the position of the pointer and moving coil assembly is to one side of center when no voltage is applied.

Furthermore, compensation for temperature errors has been greatly simplified by using a zero center instrument. For example, with no compensation, the percentage of error encountered in an instrument increases directly in proportion to the deflection from electrical center and at the high end of the deflecting scale, the error is considerably greater in instruments that have an electrical center suppressed below the end of the scale. Thus if a prior instrument had a effective scale, as compared to the present instrument with a 100 efiective scale, the prior instru-- ment would have to be depressed about 50". Therefore the distance from electrical center to maximum deflection would be whereas in the present instrument it is only 50. As a resuit, with no compensation there would be three times as much-errorin the suppressed center instrument as in the present instrument at maximum deflection. Therefore, compensation can be accomplished in the present instrument by the use of the appropriate [non-temperature] zero temperature co-eflicient-resistor with a restoring coil, whereas such would not be-as effective in the prior suppressed center structures.

It should be noted that the deflecting coil utilizes the [full available] major flux, both incoming and outgoing through the core andthe restoring coil uses the major main flux also, in contrast to prior instruments wherein the restoring coil uses only leakage flux, or each coil uses half of the [main] "major flux.

The terms front, rear, horizontal, vertical, fore and aft direction and the like are used herein and in the appended'claims to denote relative positions of the parts, and not finite positions, for convenience in description. The various resistors, including 5|, may be located'remote from the other partsof the instrument, and for clearness, have been omitted in Figs. 1 to 4, as their physical location is, as is well known, a matter of convenience orchoice.

I claim:

1. An' instrumentof the direct current moving coil type and comprising a horizontally disposed horseshoe magnet having its arms extending forwardly, a pair of generally'channel shaped pole pieces in fixed relation to the arms of the magnet, respectively, with their-sides extending horizontally, said pole pieces opening toward and being in spaced relation to 'each other to define a major flux path, a horizontal generally circular core, means extending rearwardly from the core and fixedly supporting the core between the pole pieces in spaced relation thereto and with. portions of the core extending partway within the open channels of the pole pieces, a pair of relatively axially adjustable bearings coaxial with the core and arrangedoneabove and one below the core; pivot means mounted in said bearings,- a deflecting coil oarriedby the pivot means with its axis horizontal and intersecting the axis of the pivot means'at right angles, said'coil having an axial passage of greater height and length than the height and outer diameter respectively of the core for accommodating the core within the coil with clearance in oscillated positions of the coil, said coil extending between the core and pole pieces with clearance relative to the pole pieces, and restoring means for the coil rigid therewith at right angles thereto and adapted to encircle arm portions of the core, said coil and restoring means being removable as a unit from the [magnet] pole pieces and core [assembly] without disturbing them [the magnetic flux circuit of said assembly] 2. An instrument according to claim 1 and further characterized in that'said core has a central aperture and an air gapin its forward portion and said restoring means is a restoring coil which is carried'by the pivot means and has its axis horizontal and spaced forwardly from the pivotal axis and said restoring coil has a passage therethrough which accommodates respectively, the said arm'portions of the core as the restoring co'il oscillates about the pivotal axis, and the .said

restoring coil isof less width axially than said air gap, whereby the assembled coils and pivot meansmay be removed forwardly from thedevice without disturbing the [magnetic circuit] pole pieces and core.

3-. An electrical instrument of the moving coil type, comprising a magnet having opposed chairnel' shaped pole pieces with the flanges of the channels facing each other and spaced apart in the same planes, a magnetic core centrally located between said pole pieces and having circular external peripheral surfaces [uniformly] symmetrically, spacedfrom the webs of the channels [in the common plane thereof] and provid-- ing spaced arms directed toward each other, a coil assembly including a deflecting coil pivoted on an axis generally centrally of the core, said coil being looped about the core and operatively related to the channel flanges so that opposite sides or" the coil remain in substantially uniform cutting relation to fluxlines passing between the flanges as the coil assembly is turned through'an arc of at least said coil assembly also including a restoring coil fixed to the deflecting coil normal thereto and receivable between the arms of the core so as to encircle said arms in such turned positions of the coil assembly, said ar rangem-ent enabling the coils to be assembled'as a unit into operative relationship to [the pole pieces and core] andwithout disturbing the [the magnetic circuit afforded by the magnet and core] pole pieces and core.

4. An electrical instrument ofthe moving coil type, comprising a magnet having opposed channel shaped pole pieces extendingin a fore and aft direction with the flanges of the channels facing-each other and-spaced apart in the same planes, a magnetic core having a central aper ture with'an upright axis, the core being centrally located between said pole pieces and having its external peripheral surfaces lying between said flanges and spacedtherefrom and from the webs of the channels [in the common plane] thereof and providing spaced arms directed ward each other forwardly from said axis, the webs ofthe channels being spaced apart from each other a distance greater than the width of the core throughout those portions of the'webs which are forward of said [pivoted] upright'axls, a coil assembly including a deflecting coil having a pivotal axis normal to the axis of the coi-l'an'd generally parallel to the axis of the aperture, said coil being loopedabout the core 'in spaced relation thereto and to the channels and normally occupying a neutral position in which [its] the coil'axis [is normal to its pivoted axisand] ex tends in said fore and aft directon, the core and channel shaped'p'ole pieces being related-to render the flux path substantially uniform'coex tensive with the'outermost limit of the path gen erated by-rotating the deflecting coil'through at least 45 in opposite directions from said neutral position, said coilassembly also including are storing coil fixedto the deflecting coil normal thereto and'receivable between the 'arms'of the core so as to encircle said arms in turned positions of the -coil assembly, said arrangement enabling the coils tobe assembled as a unit into operative relationship to [the pole pieces and core] and without disturbing the pole 'pieces [magnetic circuit afforded by the magnet] and core.

5. In an instrument of the directcurrentmo'w ing coil'type, a magnetic assembly complete in and of itself and'including a pair 'ofspace'd pole [faces] pieces and a core piece in-fixedspaced relation thereto in the major flux'path therebe= tween, a moving coilassembly complete-inane ofiitself and including a deflecting coil and pivots therefor and fixedly secured thereto, the deflect ing coil being adapted to lie within the major flux path between the pole pieces and core in spaced relation to the core and pole pieces and with its pivotal axis normal to the [major flux] path between the pole pieces and being receivable in said flux path and removable therefrom while the coil is in the moving coil assembly and while the magnetic assembly is in assembled condition, bearings for the pivots operable to be engaged with the pivots of the movin coil assembly, respectively, and to oscillatably support the assembly with the deflecting coil in said flux path and in spaced relation to the pole pieces and core, said deflecting coil having its axis [normally] extending at right angles to its pivotal axis and normally lying across the [major flux] path between the pole pieces in a neutral position of said deflecting coil, said pole pieces and core being shaped relative to each other to render the major flux path substantially coextensive with the outermost limits of the path generated .by rotating the [deflectionl deflecting coil through an angle of at least 45 in each direction from its neutral position, whereby said coil assembly is operatively related to the magnetic assembly in a manner to enable uniform scale deflection throughan arc of 90 and greater, and means to restore the moving coil assembly to starting position.

6. In an electrical instrument of the direct current moving coil type, a magnetic assembly comprising a permanent magnet, a pair of laterally spaced pole pieces, a core between and in fixed spaced relation to the pole pieces, said pole pieces and core defining a coil receiving space which comprises the major flux path and. which is open at the front, relatively axially adjustable upper and lower axially aligned bearings above and below the pole pieces and in fixed lateral relation thereto, a moving coil assembly including a defleeting coil and a restoring coil, upper and lower axially aligned pivots fixedly secured thereto and receivable in the bearings, respectively, the axis of the deflecting coil being at right angles to the pivotal axis, and normally extending forwardly [across the major flux path] in a neutral position of said deflecting coil, said core and pole pieces being shaped relative to each other to render the major flux path substantially uniform coextensive with the outermost limits of the path generated by rotating the deflecting coil through an angle of at least 45 in each direction from its neutral position, said deflectin coil having a central passage and being receivable into said space from the open front, and being adapted to pass into surrounding relation to the core and into spaced relation to the pole pieces and core when so received, whereby said coi1 assembly is operatively related to the magnetic assembly in a manner to enable uniform scale deflection through an angle of 90 and greater.

7. An instrument according to claim 6 and further characterized in that the restoring coil is fixedly carried by the moving coil assembly, the axis of the restoring coil being at right angles to and spaced from the axis of the pivots and at right angles to the axis of the deflecting coil, saidcore having a central aperture and an air gap at its forward portion connecting therewith and dividing the core into two integral arm portions between the ends of which the restoring coil may be passed without disturbance of the magnetic [circuit] assembly, said restoring coil having a passage therethrough and surrounding the core for accommodating the arm portions of the core in spaced relation thereto when the coil assembly is swung about its pivotal axis out of neutral position.

8. In a ratio meter, a first loopshaped coil; a second loop-shaped coil fixedly secured to the first coil, one side of the second coil spanning the space encompassed by the first coil; means mounting said coils for pivotal deflecting movements in predetermined paths, said means being operable to release the coils for removal as a unit; a single, magnetic flux-producing means providing a uniform total flum density acting on said first coil throughout its path of movement, and providing a nonuniform flux density acting on the second coil throughout its path of movement, causing the deflection of the coils to be proportional at all times to the ratio of currents which may flow in said coils, said magnetic flux-producing means including a magnet, including spaced, oppositely disposed pairs of spaced pole pieces for said magnet, and including a C-shaped magnetic core, said core extending around the said one side of the second coil and being located in spaced flux-receiving relation with the magnet pole pieces and between the latter, said pole pieces and core providing an intervening space to receive the first and second coils in difierent deflected positions thereof; and means supporting the core solely at a location wholly to one side of the pivotal axis of the coils, said magnetic flux-producing means forming a linear passage between the ends of the core, and between the pole faces and core at the other side of the coil axis, in a direction away from the core-supporting means, said passage having transverse dimensions greater than the corresponding dimensions of the coils to enable the coils to be removed without requiring movement between the pole pieces and core.

9. The invention as defined in claim 8 in which the magnetic flux-producing means provides flux in a pair of opposite arcuate paths each of sub- 'stantially extent, for traversal by opposite portions of said first coil, and provides flux in an arcuate path of substantially 90 eatent, for traversal by said second coil, thereby to enable the coil deflection of the ratio meter to be substantially 90. 10. The invention as defined in claim 8 in which the uniform total flua: density of the flux-producing means includes as a component the nonuniform flua' density acting on the second coil, the flux-producing means providing arcuate paths traversable in part by both said coils.

KNUD J. KN'UDSEN.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS Number Name Date 1,141,523 Brogger June 11, 1915 1,171,907 Trent Feb. 15, 1916 1,375,837 Foster Apr. 26, 1921 1,633,912 Vawter June 28, 1927 1,779,347 Vawter Oct. 21, 1930 1,804,330 Faus May 5, 1931 1,918,023 Faus July 11, 1933 2,346,683 Hickok Apr. 18, 1944 2,391,168 Knudsen Dec. 18, 1945 FOREIGN PATENTS Number Country Date 198,182 Great Britain a- May 21, 1923 427,532 Great Britain Apr. 25, 1935 

